Very low birthweight (VLBW) infants are unable to feed orally for weeks after birth and are maintained on parenteral nutrition. The main source of calories during this period is (Intralipid), a 10% soybean oil emulsion. Clearing of lipids is, however, less efficient in VLBW infants (less than 32 weeks gestation) than in infants greater than 33-40 weeks gestation. Parenteral feeding of lipid before adequate clearing has developed leads to severe compolications such as chronic liver disease, pulmonary embolism and death. It is not known a. whether there are differences in clearing ability between VLBW infants 26-32 weeks gestation; b. whether prolonged lipid infusion affects the clearing mechanisms; c. what is the level of lipolytic activity - measured as serum post heparin lipolytic activity (PHLA) in this gestational age group; d. to what extent do extra hepatic and hepatic lipases contribute to PHLA. We aim to answer these questions by investigating the ontogeny of heaptic and extrahepatic lipases in fetal and newborn rats. We will investigate the questions: 1. Is there a relationship between level of serum PHLA, triglyceride clearing, gestational age and postnatal age? 2. To what extent do extrahepatic and heaptic lipases contribute to serum PHLA in VLBW infants? 3. Are there developmental changes in the ratio between the two lipases? 4. Does prolonged Intralipid infusion affect serum PHLA activity and triglyceride clearing? 5. Does the method of parenteral infusion affect the level and source of serum PHLA? i.e., does constant low heparing concentration in the infusion fluid (used to prevent clotting in certain infants) affect the level or serum PHLA and the extent of triglyceride clearing? In animal studies we will investigate the ontogeny of lipoportein lipase and heaptic lipase in newborn rats and whether these lipases can be precociously induced by corticosteroids and lipd clearing in the newborn can be improved by the precocious induction of heaptic and lipoprotein lipases. As a result of these studies we aim to develop rapid, non-invasive and highly accurate tests to predict and monitor lipid clearing ability in the VLBW infant.